This invention relates to a graphic processor based on a bit-map method and, particularly, to a graphic processor suitable for graphic data transfer and conversion processes in a display memory.
Conventional graphic processors having their graphic processing functions fabricated in integrated circuits, are disclosed in, for example, U.S. patent application Ser. No. 727,850 filed on Apr. 26, 1985 and U.S. patent application Ser. No. 686,039 filed on Dec. 24, 1985. These graphic processors are designed to express graphic data corresponding to one picture element or pixel by using a plurality of bits.
Generally, a graphic processor deals with data in word units, e.g., 32-bit words, and the number of bits used to express a pixel is less than the number of bits of a word in many cases. Accordingly, when a graphic processor of 32-bit word processes graphic data in the form of 4-bits per pixel, it can treat a maximum of eight pixels with one word.
The above mentioned graphic processor of patent application Ser. No. 727,850, even though it has a 32-bit word structure, deals with graphic data in units or a pixel. Therefore it needs to repeatedly perform a writing operation or transfer operation for plurality of of times the number of which depends on the number of pixels even in such writing or transferring graphic data of consecutive pixels within a word. This imposes a problem of an increased number time that there must be access to the display memory in which graphic data is stored, and as a result, a lowering of the processing speed.
Graphic processors of this type are intended to display, in many cases, graphic figures in color or multiple tones, and when such color or multi-tone graphic data is printed on a black-and-white printer, the graphic data needs to be converted into 2-level (or binary) graphic data. Conversely, in the case of a combination of a black-and-white graphic figure on a processor and a color printer, the 2-level graphic data needs to be converted to multi-tone graphic data.
These data conversion processes are conventionally implemented pixel-by-pixel on a software basis, which expends several .mu.s to several tens .mu.s per pixel. This imposes a problem of considerable time consumption in data conversion for all pixels.
A graphic processor which implements enlargement, reduction, rotation, etc. for the original image data, while interpolating the original image data is known. An example of the interpolation process for image data including enlargement and reduction of figures is described in an article entitled "Performance Evaluation of Various Enlargement/Reduction Methods for 2-level Image Data and Method of Improving the Processing Speed", pp. 920-925 in the publication of Information Processing Society of Japan, Vol. 26, No. 5, published in September 1985. In this known technique to accelerate the process, the integral coordinate interval of transfer source data is divided four ways in each of the x and y directions. Further, interpolated data, each determined from whether the four pixels are black or white around an intermediate coordinate position corresponding to the transfer destination coordinates, is prepared as a table in advance.
The above-mentioned prior art is pertinent to the interpolation of 2-level image data (monochrome image data), and does not deal with the color image interpolation in which a pixel is expressed in a plurality of bits. Therefore, the enlargement and reduction process for color image data is compelled to base the interpolation on the software using a CPU or the like, which imposes a problem in enhancing the speed of the process.